The femtosecond laser two-photon processing technology, known for its flexible three-dimensional (3D) high-precision machining capabilities, is commonly employed for the high-precision fabrication of various microdevices. However, existing single-point scanning strategies exhibit low processing efficiency, which significantly limits further development of this technology. To address this issue, researchers have proposed several parallel processing techniques, including those based on microlens arrays, diffractive optical elements, and multi-beam interference methods. Although these methods demonstrate certain advantages in improving the processing efficiency, they still possess some significant limitations. Liquid crystal on silicon spatial light modulators (LCoS-SLMs) can freely modulate the wavefront of a beam, enabling the generation of multi-foci arrays and various structured lights. The combination of spatial light-shaping technology with femtosecond laser two-photon polymerization can effectively enhance both the processing efficiency and flexibility. Airy beams have been widely applied across multiple fields owing to their self-accelerating, non-diffraction, and self-healing characteristics. In a previous study, two symmetric Airy beams were directly generated using LCoS-SLM, achieving the efficient fabrication of 3D microgripper structures via a single exposure. Building upon this foundation, this study integrates dynamic holographic processing technology with femtosecond laser two-photon polymerization to further enhance the processing efficiency and flexibility, advance the development of two-photon processing technology, and broaden its application scope.

The femtosecond laser source used in this study is a mode-locked Ti∶sapphire ultrafast oscillator with key parameters, including a central wavelength of 800 nm, pulse width of 75 fs, and repetition frequency of 80 MHz. After passing through the expansion system, the laser beam is directed onto the LCoS-SLM using a grazing incidence technique with mirrors. Mechanical shutters and power attenuators are employed to control the on/off states and power levels of the laser, respectively. Computer-generated dynamic holograms are loaded onto the LCoS-SLM to modulate the wavefront distribution of the laser light. The modulated laser then sequentially passes through two lenses with focal lengths of 600 mm and 200 mm. The conjugate focal planes of the two lenses form a 4f system for spatial filtering and beam reduction. Finally, a microscope objective lens focuses the laser for processing. The 3D piezoelectric stage supports the sample and offers high-precision motion control, with a coaxial charge coupled device (CCD) employed for real-time imaging and monitoring of the entire processing procedure. The reflective LCoS-SLM used has a resolution of 1920 pixel×1080 pixel with a pixel pitch of 8 μm. Each pixel can independently modulate the wavefront of the beam within its area, with a modulation grayscale range from 0 to 255, corresponding to a phase range from 0 to 2π. MATLAB software is used to generate computer-generated holograms, which are then compiled into graphic interchange format (GIF) dynamic images. The 3D piezoelectric stage has a movement range of 200 μm×200 μm×200 μm, with a positioning accuracy of less than 1 nm and repeatability of less than 5 nm, ensuring the precision and stability of micro-nano processing. The objective lens employed in the experiments is a 60× oil immersion lens, with a numerical aperture (NA) of 1.35. A commercially available negative photoresist is used.

The directly generated symmetric Airy beam holograms are rotated to create a GIF dynamic image, which is then loaded onto the LCoS-SLM. With the laser power set to 70 mW, the rotation angle can be controlled by adjusting the exposure time, resulting in bowl-shaped structures with varying aperture sizes (Fig. 5). By dynamically and holographically processing multiple symmetric Airy beams with different parameters, micro-flowers are rapidly fabricated by adjusting the exposure time, with an eight-petal flower requiring only 1.4 s for processing. The advantage of dynamic holographic processing is its ability to rapidly realize complex 3D structures without relying on the motion conditions of the 3D moving stage, thereby effectively reducing the equipment costs of the experimental system. Furthermore, “open-close controllable” 3D micro-flower fabrication is achieved by integrating self-assembly techniques and appropriately controlling processing parameters (Fig. 6). Finally, a composite motion processing technology that combines dynamic holography with a 3D moving stage is proposed. By utilizing the dynamic holographic technique of Airy beams, along with the horizontal movement of the stage, microspring structures with varying numbers of turns are rapidly processed. Annular structures with different petal counts are fabricated by altering the motion of the moving stage to a circular motion and adjusting the radius of this motion (Fig. 8). The combination of 3D optical field dynamic holography and moving stage motion methods provides various options for designing 3D structures, thereby enhancing both design flexibility and processing diversity.

This paper presents a composite processing technology that integrates dynamic holography with the motion of a 3D moving platform. By rotating the hologram, dynamic holography enables the rapid fabrication of 3D multi-petal “flower” structures. Furthermore, by incorporating capillary self-assembly techniques, the “opening” and “closing” of these flowers can be controlled. Through the dynamic variation of the hologram and real-time motion of the 3D moving platform, 3D microspring structures are efficiently fabricated. This technology offers a high processing efficiency and fabrication flexibility, supporting the precise manufacturing of complex structures over large areas. In the future, the possibility of single-exposure fabrication of arbitrary 3D structures can be explored based on dynamic femtosecond laser holographic processing technology. In addition, combining 3D structured light fields with iterative computational holography has the potential to enhance femtosecond laser processing technology, effectively improving both processing efficiency and flexibility.